Building a software product is fundamentally different than implementing a software solution for a specific customer. While this might sound like common knowledge, a surprisingly big number of people in our industry just do not grasp it.
As a product manager, you need to make sure that you are strategically developing a product that can be sold to n and not to 1 customer. If you concentrate on just one key account, then you are implementing a software project, not a product, which is by no means wrong, it is just a different business.
Inevitably, the voice of your biggest accounts is louder and has to be considered accordingly. Similarly, if a specific feature can close a deal with a serious prospect, you need to consider it too. Ongoing development has to be financed somehow, right?
Nevertheless, your primary goal and responsibility as a product manager is not to be friends with the VP Sales in the short term, but to make sure that (s)he has a great product to sell in the medium term.